The T-joint formed by upper and lower crankcase members and a crankshaft seal member is difficult to seal. The upper and lower crankcase members have mating surfaces that move perpendicular to one another as the crankcase members are assembled, and a seal between the crankcase members is readily compressed during that process. However, as the crankshaft seal member is assembled to the crankcase members, it moves parallel to the common lateral cylindrical surface defined by the assembled crankcase members; thus a seal projecting from between the crankcase members to engage the crankshaft seal member is subjected to shear forces by the crankshaft seal member.